With the development of mobile communication technologies, more and more attention has been paid to the IP Multimedia Subsystem (IMS). The IMS is a multimedia control/call control platform over a PS domain, which supports session type and non-session type multimedia services, and provides a general service enabling platform for future multimedia applications. The IMS uses the PS domain to bear and transmit multimedia signals and can be regarded as being superposed over the PS domain which serves the IMS.
Based upon the IMS, the provider can deploy numerous services, such as stream media service, visual telephone service, Push to Talk over Cellular (PoC) service, presence service, Instant Messenger (IM) service, and Combined Circuit Switched and IP Multimedia Subsystem Sessions (CSI) service.
For all PS domain based services, including the IMS service, the current application protocols require that all participating terminals shall have activated a PS domain during deployment of service. On this premise, any service initiator may first activate the PS domain on its own initiative when initiating service, but it cannot ensure whether the opposite terminal has activated the PS domain. Also in the case that the terminal of the service initiator (the terminal may activate the PS domain on its own initiative after deciding to initiate the service) has activated the PS domain but the opposite terminal has not activated the PS domain, the service cannot be transmitted based upon the PS domain, and the PS domain based services, including the IMS service, cannot be implemented.
In order to ensure smooth deployment of the PS domain based service, existing systems utilize a terminal to activate a PS domain on its own initiative each time it is powered on so as to register with an IMS domain. Therefore, the terminal supporting the PS domain based service in a communication system can be kept at any time in the status of PS domain being activated. These systems can ensure smooth deployment of the PS domain based service.
However, the inventors of the present invention have found that at least the following drawbacks exist in the existing systems which are not practical in many applications. For example, in practical applications, not all terminals are expected to activate a PS domain when they are powered on. Consequently, existing systems may have negative influences on users' experience.